Project Summary The beginning of the 21st century has seen the evolution and dissemination of highly resistant Gram-negative pathogens, especially including carbapenem resistant Enterobacteriaceae (CRE), including Klebsiella pneumoniae and Escherichia coli, as well as Acinetobacter baumannii and Pseudomonas aeruginosa. This project entails the development of new antibiotics, in the form of carbapenems, to counteract these resistant microorganisms. The carbapenems are modified in specific ways to improve penetration of the Gram- negative bacterial outer membrane, to elude 21st century carbapenemases, and to improve binding to their specific targets, the penicillin binding proteins. Strong initial data supports the hypothesis that we can successfully modify key properties, such as carbapenemase stability and permeation of Gram-negative pathogens through appropriate structural changes. It is also desired to render the new antibiotics more specific for their selected pathogen. This concept is also supported by strong initial data, demonstrating that a highly atypical modification of the carbapenem scaffold can improve activity against Mycobacterium tuberculosis. We propose to design molecules to specifically target the L,D-transpeptidase of Mycobacterium tuberculosis, to enable the generation of a carbapenem which can selectively eradicate this pathogen without adversely affecting commensal microbiota. Numerous collaborations are in place with leading academic and commercial scientists to assess antibacterial potency, carbapenemase resilience, target transpeptidase binding, transport, and cytotoxicity. Initial results of these assays are promising, with several newly designed carbapenems displaying properties superior to meropenem, the best current commercial carbapenem antibiotic.